It sounds like a tiny stream of gas bubbling, this would sound like a ticking noise.
Tell me more about the type of battery and charger you have.
battery look like a box 85aph leisure battery charger is grey have 2 croc clips one for + one for - has switch for fast or slow charge, say when charging and whenn full (so it say with green ligth I dont trust it) aprt from that I know not much m8.
i used the battery that was making the noise today an a few houses and it worked ok, usual stutter on the ecoflow didnt have to stop move wire today which was a bonus it some times goes dead totally (highly annoying that is I can tell you)